The present invention pertains to the mobile wireless communication technology and pertains in particular to the technology for avoiding interference between adjacent frequencies occurring on cell boundaries or sector boundaries in a mobile wireless communication system using an OFDMA (Orthogonal Frequency Division Multiple Access) scheme.
Accompanying with the advancement of mobile wireless communication technology, it is expected that a ubiquitous network will be implemented which releases users from the constraints of the location and moving velocity when using a mobile station and with which users can connect more freely, anytime and anywhere.
A mobile wireless communication system comprises a plurality of base station apparatuses and a plurality of mobile stations communicating wirelessly with the base station apparatuses. The plurality of base station apparatuses are arranged decentrally to form areas called “cells” where wireless communication is possible, in ranges where radio waves transmitted from the respective base station apparatuses can reach. Using a directional antenna, a base station apparatus may also divide a cell angularly into a plurality of ranges called “sectors” where radio wave can reach. As a sector configuration, three-sector configuration dividing a cell into three, and six-sector configuration dividing a cell into six are common. It is also possible to consider a sector divided angularly using the directivity of the antenna as a cell, and what includes both concepts is often called a “cell” in the present invention.
A wireless communication system is provided with a mechanism for continuing the communication by repeating handover between base station apparatuses in response to the movement of a mobile station. In this way, cells formed respectively by a plurality of base station apparatuses overlap so that the wireless communication system can maintain wireless communication even if the mobile station moves. In the overlapping area formed by two base station apparatuses, wireless communication between the mobile station and one base station apparatus of them interferes with the communication of the other one. Interference is radio waves disturbing the communication of the mobile stations, and causes signal quality degradation or throughput degradation in wireless communication.
For example, the technology for avoiding or controlling inter-cell interference is disclosed in JP-A-2008-061250, JP-A-2009-021787, and JP-A-2009-044397.
On the one hand, in terms of standardization, 3GPP (Third Generation Partnership Project) which is one of standards bodies proposes a wireless scheme based on the OFDM (Orthogonal Frequency Division Multiplexing) scheme called “LTE (Long Term Evolution).” The document 3GPP TS36.331 6.3.2 (Radio resource control information elements) discloses the technology for changing the antenna transmission mode of a mobile station via an instruction from a base station in LTE.
On the other hand, the IEEE which is another standards body proposes in IEEE 802.16e, a wireless scheme based on OFDM called “Mobile WiMax (Mobile Worldwide Interoperability for Microwave Access)”, and IEEE 802.16m advocates the technology called “FFR (Fractional Frequency Reuse)” in the document Mobile WiMax-Part I: A Technical Overview Performance Evaluation, Section 4.2: “Fractional Frequency Reuse”.
IEEE 802.16m discusses FFR also in the IEEE 802.16m System Description Document IEEE 802.16m-08/00 3r6, Section 20.1: “Interference Mitigation Using Fractional Frequency Reuse”. Another section of the same document, IEEE 802.16m System Description Document IEEE 802.16m-08/00 3r6, Section 20.2.2: “Multi-ABS Joint Antenna Processing” describes network MIMO (Multiple Input Multiple Output) in which a plurality of base stations cooperate.